Ultrasonic diagnosis makes it possible to display the pulsation of the heart or the movement of an embryo in real time by a simple operation of bringing an ultrasonic probe into contact with a body surface. In addition, since the ultrasonic diagnosis is highly safe, the test may be repeatedly performed. In addition, the system size is small compared with other diagnostic apparatuses, such as an X ray, a CT, and an MRI, and a test at the bedside can also be easily performed. For this reason, it can be said that the ultrasonic diagnosis is an easy diagnostic method. An ultrasonic diagnostic apparatus used in the ultrasonic diagnosis varies in various ways with the type of a function that the ultrasonic diagnostic apparatus has. As a small ultrasonic diagnostic apparatus, an ultrasonic diagnostic apparatus that is so small that it can be carried with one hand has been developed. In addition, since the ultrasonic diagnosis does not cause radioactive exposure unlike the X ray, the ultrasonic diagnosis may also be used in an obstetric treatment, a remote medical treatment, and the like. In addition, a recent ultrasonic diagnostic apparatus may collect three-dimensional biological information (volume data) by spatially scanning the inside of the tested body using an ultrasonic probe with a two-dimensional array in which ultrasonic vibrators are arrayed in a two-dimensional manner.
A conventional technique for the purpose of speckle reduction in the ultrasonic diagnosis includes filtering processing including a combination of multi-resolution analysis and a nonlinear anisotropic diffusion filter. In the nonlinear anisotropic diffusion processing, different processings are applied to edge portions and the other portions, so that an image with edge emphasis and speckle reduction can be obtained. In the multi-resolution analysis, processings proceed from macro-scale processing to more local processing in order, and this enables fast and efficient processing.
However, when the state of an embryo is observed particularly in a three-dimensional manner with the above conventional filtering technique, relatively large recesses and protrusions on the surface of the face of the embryo are detected as edges in a lower level processing of the multi-resolution analysis. Accordingly, since the edges of recesses and protrusions are emphasized as described above, they may be incorrectly recognized as edges in an upper level processing of the multi-resolution analysis. As a result, the edges may be unnaturally emphasized in an output image. On the other hand, small edges that can be detected only in the upper level, such as fingers, are affected by lower speckle reduction, and therefore, it may be difficult to detect them as edges in the output image.